So, how many official continuities do we count? I mean, most listed aren't really divergent realities as much as alternate reboot universes. For example, Halloween 2007 isn't divergent to the Slasherverse as it is a new version of Michael all together, unlike 2018 where it kinda branches, but for the sake of it, I'm listing in thus comment anyway.
-Slasherverse
-Halloween III/Halloween H40 [I'm gonna say they're linked]
-Darkman (TV Pilot)
-Bates Motel (Movie)
-Wes Craven's New Nightmare [Real World]
-Halloween H20 [Potentially Canon]
-28 Days/Transformers/Friday the 13th (2009)
-Texas Chainsaw Massacre (2003)
-Toolbox Murders (2004)
-The Amityville Horror (2005)
-Black Christmas (2006)
-Halloween (2007)
-A Nightmare on Elm Street (2010)
-Texas Chainsaw 3D [Taken as Canon]
-Bates Motel (TV Series)
-Amityville: The Awakening [Real World]*
-The Amityville Murders
-Child's Play (2019)
-Black Christmas (2019)
-The Amityville Curse
*While Amityville: The Awakening is set in a world where the original films and reboot are fiction, it doesn't have the same meta-understanding of parallel universes accessed through the lens of fiction that Wes Craven's New Nightmare does, if that makes sense. You can put it in the same continuity I suppose.